Thus, we might expect that a study of the various glume 
phenotypes of modern maize would be revealing as to 
the past and possible further evolution of this glume dur- 
ing domestication. 
Three dominant or semi-dominant genes which affect 
principally the outer pistillate glume were included in 
this study. They are as follows: (1) Papyrescent (Pn 
gene on chromosome-7); (2) Tunicate (Zw gene on 
chromosome-4); (8) Vestigial glume (/¢ gene on chrom- 
osome-1). These genes were studied in heterozygous con- 
dition after they had been incorporated, by repeated 
backcrossing, into an isogenic background of a sweet 
corn (maize) inbred (Purdue 389). Their effects on the 
histological structure of this glume were examined in 
material prepared in the following manner: Normal 
(typical) and variant specimens were fixed at 18 days 
after pollination. ‘This material was later embedded in 
paraffin, according to the usual procedure, and then cut 
in cross-section at 12 uw. The sections were then stained 
by the standard safranin-fast-green technique. Finally, 
a projection apparatus was used in making tracings from 
comparable slides. 
Normal glumes. The glumes and other floral bracts of 
modern maize are so reduced that the mature grain 
emerges naked above them. Protection for the grain, 
which is provided by long floral bracts in most other 
grasses, is supplied by husks (modified leaf-sheaths) borne 
below the pistillate inflorescence (ear) on a condensed 
branch (shank). 
The normal glume has papery lateral wings (Plate LX, 
fig. 3) and the entire structure is homologous to a leaf- 
sheath with sheath-auricles. The glume-sheath, which is 
the counterpart of the leaf-sheath, may be coriaceous in 
texture (in many South American varieties) or, more 
commonly, it may resemble its counterpart in teosinte 
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